Measurement of Flow-Mediated Vasodilation of the Brachial Artery A Comparison of Measurements in the Seated and Supine Positions

New device for assessment of endothelial function: plethysmographic flow-mediated vasodilation (pFMD)

Measurement of flow-mediated vasodilation (FMD) in the brachial artery by using ultrasound is a well-established technique for evaluating endothelial function. To make the measurement quicker and simpler than the measurements of conventional ultrasound FMD (uFMD), we have developed a new noninvasive method, plethysmographic FMD (pFMD), to assess vascular response to reactive hyperemia in the brachial artery. The aim of this study was to determine the accuracy of measurement of pFMD in comparison to that of measurement of conventional uFMD. This study was a multi-center, cross-sectional study. We compared pFMD by a new device using cuff pressure and volume with conventional uFMD using ultrasound in 50 men (mean age, 41 ± 9 years). pFMD significantly correlated with conventional uFMD (β = 0.59, P < 0.001). In Bland-Altman plot analysis of pFMD and conventional uFMD, the mean difference of pFMD and conventional uFMD was 0.78%, and limits of agreement (mean difference ±2 standard deviations of the difference) ranged from -4.53% to 6.11%. We demonstrated validity of the new method for measurement of pFMD, which can automate the evaluation of endothelial function in a short time. Measurement of pFMD is simpler than measurement of conventional uFMD and may have reduced artificial bias compared to that of conventional uFMD measurement (URL for Clinical Trial: https://ethics.hiroshima-u.ac.jp/site/wp-content/uploads/2022/12/eki_giji20221213.pdf . Registration Number for Clinical Trial: E2022-0131).

Endothelial function in response to exercise in the cold in patients with coronary artery disease

BACKGROUND

Regular long-term physical exercise has favourable effects on endothelial function in patients with coronary artery disease (CAD). However, the effects of an acute exercise bout in the cold on endothelial function are not known.

METHODS

At first, the effects of moderate-intensity aerobic lower-body exercise were assessed in CAD patients (n = 16) in a neutral [+22°C] and cold [-15°C] environment. Secondly, responses to static and dynamic upper-body exercise in a neutral [+22°C] and cold [-15°C] environment were investigated in CAD patients (n = 15). All experiments were performed in a random order. Endothelial function was measured by flow-mediated dilation (FMD) of the brachial artery in response to reactive hyperaemia, before and after the exposures in a neutral environment.

RESULTS

No significant temperature*exercise*condition (pre-post) interaction was observed in FMD% when comparing rest versus aerobic exercise or static versus dynamic upper-body exercise. Relative reactive hyperaemia during FMD protocol, measured by changes in shear rate, was elevated after rest compared to aerobic exercise (p = .001) and after static compared to dynamic upper-body exercise (p < .001). However, no significant temperature*exercise*condition interaction was observed when FMD% was normalized for shear rate.

CONCLUSIONS

Endothelial function to an acute bout of exercise among CAD patients was not modified by the environmental temperature where the exercise was performed. The present findings argue against the hypothesis that exercise in cold environmental conditions impairs endothelial function in patients with CAD.

The Pilot Study of Evaluating Fluctuation in the Blood Flow Volume of the Radial Artery, a Site for Traditional Pulse Diagnosis

Background: Radial artery (RA) pulse diagnosis has been used in traditional Asian medicine. Blood pressure (BP) and pulse rate related to heart rate variability (HRV) can be monitored via the RA. The fluctuation in these parameters has been assessed using fast Fourier transform (FFT) analytical methods that calculate power spectra. Methods: We measured blood flow volume (Volume) in the RA and evaluated its fluctuations. Normal participants (n = 34) were enrolled. We measured the hemodynamics of the right RA for approximately 50 s using ultrasonography. Results: The parameters showed the center frequency (CF) of the power spectrum at low frequency (LF) and high frequency (HF). More than one spectral component indicated that there were fluctuations. The CF at LF for Volume was significantly different from that for vessel diameter (VD); however, it was significantly correlated with blood flow velocity (Velocity). On the other hand, the CF at HF for Volume was significantly different from that for Velocity; however, it was significantly correlated with VD. Conclusion: It is suggested that fluctuation in the Volume at LF of RA is influenced by the fluctuation in Velocity; on the other hand, fluctuation in the Volume at HF is influenced by the fluctuation in VD.

Assessment of endothelial function. History, methodological aspects, and clinical perspectives

In 1986, endothelial function was measured for the first time in patients with atherosclerotic coronary arteries. Since then, several methods for assessment of endothelial function, such as endothelium-dependent vasodilation induced by intra-arterial infusion of vasoactive agents using coronary angiography, Doppler flow guide wire, mercury-filled Silastic strain-gauge plethysmography, flow-mediated vasodilation, reactive hyperemia-peripheral arterial tonometry, and vascular response using an oscillometric method have been performed in humans. This review focuses on the assessment of endothelial function, including measurement history, methodological issues, and clinical perspectives.

Impact of Framingham risk score, flow-mediated dilation, pulse wave velocity, and biomarkers for cardiovascular events in stable angina

Although the age-adjusted Framingham risk score (AFRS), flow-mediated dilation (FMD), brachial-ankle pulse wave velocity (baPWV), high-sensitivity C-reactive protein (hsCRP), fibrinogen, homocysteine, and free fatty acid (FFA) can predict future cardiovascular events (CVEs), a comparison of these risk assessments for patients with stable angina has not been reported. We enrolled 203 patients with stable angina who had been scheduled for coronary angiography (CAG). After CAG, 134 patients showed significant coronary artery disease. During 4.2 yr follow-up, 36 patients (18%) showed CVEs, including myocardial infarction, de-novo coronary artery revascularization, in-stent restenosis, stroke, and cardiovascular death. ROC analysis showed that AFRS, FMD, baPWV, and hsCRP could predict CVEs (with AUC values of 0.752, 0.707, 0.659, and 0.702, respectively, all P<0.001 except baPWV P=0.003). A Cox proportional hazard analysis showed that AFRS and FMD were independent predictors of CVEs (HR, 2.945; 95% CI, 1.572-5.522; P=0.001 and HR, 0.914; 95% CI, 0.826-0.989; P=0.008, respectively). However, there was no difference in predictive power between combining AFRS plus FMD and AFRS alone (AUC 0.752 vs. 0.763; z=1.358, P=0.175). In patients with stable angina, AFRS and FMD are independent predictors of CVEs. However, there is no additive value of FMD on the AFRS in predicting CVEs.

Hemodynamic changes in the brachial artery induced by acupuncture stimulation on the lower limbs: a single-blind randomized controlled trial

Acupuncture is commonly performed at acupoints. No comparisons of quantitative physiological alterations in the brachial artery (BA) induced by the stimulation of different acupoints in the lower limbs have been performed in humans. Therefore, we investigated changes in blood flow volume (BFV) in the BA as an indicator of the physiological effects induced by stimulation at 3 points. Seventy-five healthy participants aged 33 ± 9 years (mean ± SD) were enrolled and randomly assigned to 3 groups; they received stimulation at 3 different points located on the lower limbs: ST36, LR3, and a non-acupoint. Stimulation was performed bilaterally with manual rotation of the needles. Using ultrasonography, BFV was measured continuously from rest to 180 seconds after stimulation. LR3 stimulation significantly increased BFV compared to that before needle insertion. Meanwhile, stimulation at ST36 and the non-acupoint significantly decreased BFV compared to that before needle insertion. Stimulation at LR3 elicited a significant increase in BFV compared to that at ST36 and the non-acupoint. The results suggest that the stimulation of different points on the lower limbs causes distinct physiological effects on BFV in the BA.

Novel non-invasive method of measurement of endothelial function: enclosed-zone flow-mediated dilatation (ezFMD)

Measurement of flow-mediated dilatation (FMD) is the conventional non-invasive method for assessment of endothelial function; however, it requires an expensive ultrasound system and high levels of technical skill. Therefore, we developed a novel method for measurement of endothelial function, namely, measurement of ezFMD. ezFMD estimates the degree of vasodilatation from the oscillation signals transmitted to a sphygmomanometer cuff attached to the upper arm. The objective of this study was to validate the principle underlying the measurement of ezFMD, and to evaluate the repeatability of the ezFMD measurements. We observed the blood vessel behavior and oscillometric pattern in ten subjects. When the cuff was inflated to the level of the mean blood pressure, the oscillation amplitude increased with increasing degree of vasodilatation. In experiment to evaluate the repeatability of the ezFMD measurement, the average difference between the paired measurements was 3.7 %, the standard deviation was 11.5 %, and the average coefficient of variation value for the 11 paired measurements was 23.7 %. These results suggest the validity of the principle underlying the measurement of the ezFMD for the assessment of endothelial function. And, this study suggests that the repeatability of the ezFMD measurements is superior to that of the conventional measurement of FMD.

Evaluation of the effects of acupuncture on blood flow in humans with ultrasound color Doppler imaging

Color Doppler imaging (CDI) can be used to noninvasively create images of human blood vessels and quantitatively evaluate blood flow in real-time. The purpose of this study was to assess the effects of acupuncture on the blood flow of the peripheral, mesenteric, and retrobulbar arteries by CDI. Statistical significance was defined as P values less than 0.05. Blood flow in the radial and brachial arteries was significantly lower during needle stimulation on LR3 than before in healthy volunteers, but was significantly higher after needle stimulation than before. LR3 stimulation also resulted in a significant decrease in the vascular resistance of the short posterior ciliary artery and no significant change of blood flow through the superior mesenteric artery (SMA) during acupuncture. In contrast, ST36 stimulation resulted in a significant increase in blood flow through the SMA and no significant change in the vascular resistance of the retrobulbar arteries. Additionally, acupuncture at previously determined acupoints in patients with open-angle glaucoma led to a significant reduction in the vascular resistance of the central retinal artery and short posterior ciliary artery. Our results suggest that acupuncture can affect blood flow of the peripheral, mesenteric, and retrobulbar arteries, and CDI can be useful to evaluate hemodynamic changes by acupuncture.

Impact of lipid profile and high blood pressure on endothelial damage

BACKGROUND

Endothelial damage is an early component of atherosclerosis; however, the impact of cardiovascular risk factors on endothelial function is not clearly understood. We investigated the impact of lipid profiles and high blood pressure on damage.

OBJECTIVE

Japanese male outpatients with grade I or II hypertension, along with gender and age-matched normotensive subjects (both n = 25), were enrolled. Subjects with severe cardiovascular risk factors or illness or those taking medications were excluded. Blood was sampled for laboratory analysis and endothelial function was assessed by flow-mediated dilation (FMD).

RESULTS

Total cholesterol to high-density lipoprotein cholesterol ratio (total-C/HDL-C) was inversely correlated with the FMD value and positively correlated with both malondialdehyde-modified low-density lipoprotein and high-sensitivity C-reactive protein values. Stepwise regression analysis revealed total-C/HDL-C and systolic blood pressure were significant determinants of FMD. Hypertensive subjects had lower FMD values and similar lipid profiles to normotensive subjects. Grouping subjects according to total-C/HDL-C levels showed that those with high values had lower FMD values. Hypertensive subjects with low total-C/HDL-C had similar endothelial index values to those in normotensive subjects with high total-C/HDL-C. Logistic regression indicated hypertension and high total-C/HDL-C were significantly associated with low FMD values.

CONCLUSION

Impaired endothelial function was associated with increased total-C/HDL-C values, possibly as the result of increased vascular oxidative stress and inflammation. In the early stages of atherosclerosis, the impact of both total-C/HDL-C and BP may be similar in terms of endothelial damage.

Vascular Function and Circulating Progenitor Cells in Thromboangitis Obliterans (Buerger's Disease) and Atherosclerosis Obliterans

Thromboangitis obliterans (TAO; Buerger's disease) and atherosclerosis obliterans (ASO) are associated with endothelial dysfunction. The purpose of this study was to evaluate the role of circulating progenitor cells (CPCs) in endothelial function in patients with TAO and ASO. We measured flow-mediated vasodilation (FMD), nitroglycerine-induced vasodilation, and circulating CPCs in 30 patients with TAO and 30 age- and sex-matched healthy subjects and in 40 patients with ASO. FMD was smaller in both the TAO group and ASO group than in the control group (6.6±2.7%, 5.7±3.3% versus 9.5±3.1%, P <0.0001, respectively). There was no significant difference in FMD between the TAO group and ASO group. Nitroglycerine-induced vasodilation was similar in the 3 groups. The number of and migration of circulating CPCs were similar in the TAO group and control group, whereas the number of and migration of circulating CPCs were significantly lower in the ASO group than in other groups (ASO 553±297/mL versus TAO 963±543/mL; control 1063±426/mL and ASO 36±18/hpf versus TAO 62±23/hpf; control 68±18/hpf, P <0.0001, respectively). There was a significant relationship between the number of and migration of CPCs and FMD ( r =0.43 and r =0.40, P <0.0001, respectively). FMD was impaired in patients with TAO as well as in patients with ASO compared to that in normal control subjects, and the number of and function of circulating CPCs were not decreased in patients with TAO. These findings may partially explain why there are differences in cardiovascular morbidity and mortality rates between patients with TAO and patients with ASO.

Brief effect of acupuncture on the peripheral arterial system of the upper limb and systemic hemodynamics in humans

BACKGROUND

Pulse diagnosis of the peripheral artery is an important technique in Traditional Chinese Medicine, where, in acupuncture therapy, the treatment is adjusted according to the observed changes of the pulse. We investigated the change of blood flow in the peripheral artery and the cardiac index during acupuncture treatment.

OBJECTIVES

The aim of this study is to explore the effect of acupuncture on radial and brachial artery blood flow volume and the cardiac index in healthy subjects.

METHODS

Eighteen (18) healthy volunteers were enrolled. Acupuncture was performed bilaterally on LR-3 with manual rotation of the needles. The blood pressure and heart rate were measured at rest and 180 seconds after acupuncture. Radial and brachial artery blood flow volume was monitored continuously by an ultrasound with an echo-tracking system. Cardiac index was measured by impedance cardiography. The hemodynamic parameters were measured before, during, and 30, 60, 180 seconds after acupuncture.

RESULTS

The peripheral artery blood flow volume decreased significantly during acupuncture (radial; p < 0.01, brachial; p < 0.05) but increased at 180 seconds after acupuncture (radial; p < 0.05, brachial; p < 0.05) compared with before acupuncture. The cardiac index did not change significantly after acupuncture, but systemic vascular resistance index significantly decreased (p < 0.05).

CONCLUSIONS

The present study showed that radial and brachial artery blood flow volume decreased immediately during acupuncture on LR-3 acupoint, but increased at 180 seconds after acupuncture. This reaction is attributed to the change in peripheral vascular resistance.

Radial artery hemodynamic changes related to acupuncture

BACKGROUND

Assessment of the radial pulse by palpation (pulse diagnosis) is an important diagnostic technique in Traditional Chinese Medicine (TCM), but the changes of blood flow volume in the radial artery during and after acupuncture are unknown.

OBJECTIVE

The aim of this study was to explore the changes of radial artery blood flow volume during and after acupuncture in healthy subjects.

DESIGN

This study was conducted as a pilot study utilizing a one-group intervention design.

SETTING

The study was conducted at a TCM outpatient clinic of Tohoku University Hospital.

PARTICIPANTS

Twenty-six healthy volunteers participated in the study.

INTERVENTION

Acupuncture was performed at LR-3 bilaterally with manual rotation of the needles.

OUTCOME MEASURES

Blood pressure was measured at rest and 180 seconds after acupuncture. Radial artery hemodynamics were monitored continuously with a high-resolution ultrasound echo-tracking system. The vessel diameter and blood flow volume of the right radial artery and heart rate were measured at rest, before acupuncture, during acupuncture, and 30, 60, and 180 seconds after acupuncture.

RESULTS

The systolic and diastolic diameter of the radial artery did not significantly change. Radial artery blood flow volume decreased significantly during acupuncture (mean +/- SD, 0.16 +/- 0.11 mL/sec per m(2); P < .01) compared with baseline (0.43 +/- 0.27 mL/sec per m(2)), but was increased at 180 seconds after acupuncture (0.54 +/- 0.28 mL/sec per m(2); P < .01).

CONCLUSIONS

The present study showed that radial artery blood flow volume decreased immediately during acupuncture at the LR-3 acupoint, but was increased at 180 seconds after acupuncture.

Endothelial function in subjects with isolated low HDL cholesterol: role of nitric oxide and circulating progenitor cells

Epidemiologic studies have shown that a low level of high-density lipoprotein (HDL) cholesterol is a risk factor for cardiovascular diseases. The purpose of this study was to determine the contribution of isolated low HDL cholesterol to endothelial function. Thirty-nine subjects with low HDL cholesterol who had no other cardiovascular risk factors were selected from the 5,417 participants from our population. We evaluated flow-mediated vasodilation (FMD) before and after 4 wk of treatment with the HMG-CoA reductase inhibitor pravastatin in 29 of the 39 subjects with isolated low HDL cholesterol. FMD was lower in the low-HDL-cholesterol group (n = 29) than in the control group (n = 29), whereas NTG-induced vasodilation was similar in the two groups. Pravastatin increased HDL cholesterol, urinary excretion of nitrite/nitrate, circulating levels of progenitor cells, and cell migration response to vascular endothelial growth factor in 15 subjects with low HDL cholesterol but not in 14 placebo control subjects. FMD increased in the pravastatin treatment group but not in the control group. NTG-induced vasodilation was similar before and after 4 wk of treatment in the two groups. Multiple regression analysis revealed that changes in HDL cholesterol, the number of progenitor cells, and migration of progenitor cells were independent predictors of augmentation of FMD with pravastatin. These findings suggest that low HDL cholesterol is an independent risk factor for endothelial dysfunction and that pravastatin improves endothelial function in individuals with isolated low HDL cholesterol through, at least in part, an increase in circulating progenitor cells.

Impaired endothelial function may be due to decreased aortic tetrahydrobiopterin, assessed by a new flow-mediated vasodilation in vivo in hypercholesterolemic/atherogenic mice

Tetrahydrobiopterin (BH4) is an important cofactor for endothelial nitric oxide synthase activity. The relationship between endothelial function in vivo and aortic BH4 level is not fully understood, however. In the present study, we aimed to clarify whether reduction of aortic BH4 levels contributes to endothelial dysfunction in vivo using spontaneously hyperlipidemic mice. To estimate endothelial function in vivo and in real-time state, we developed a flow-mediated vasodilation (FMV) method in mice, which measured changes in the diameter of the femoral artery in response to increased blood flow. C57BL/6 mice and apoE/low-density lipoprotein receptor double knock-out mice were fed a low-fat diet (LFD) or a high-fat diet (HFD) for 12 weeks from 6 weeks of age. HFD feeding impaired FMV in double knock-out mice, but not in C57BL/6 mice. Furthermore, HFD feeding reduced plasma NOx concentration and aortic BH4 level in double knock-out mice. Conversely, exogenous injection of BH4 (2 mg/kg) markedly increased aortic BH4 levels and restored endothelial function. In conclusion, we demonstrated that HFD feeding impaired nitric oxide-mediated endothelial function and reduced BH4 level in vivo, and that acute augmentation of aortic BH4 levels improved endothelial function. These findings indicate that BH4 is a critical determinant of nitric oxide-mediated endothelial function in hypercholesterolemia.

Measurement of hemodynamics during postural changes using a new wearable cephalic laser blood flowmeter

BACKGROUND

Patients with orthostatic hypotension have pathologic hemodynamics related to changes in body posture. A new cephalic laser blood flowmeter that can be worn on the tragus to investigate the hemodynamics upon rising from a sitting or squatting posture was developed.

METHODS AND RESULTS

The relationship between cephalic hemodynamics and cerebral ischemic symptoms in 63 subjects in a sitting, squatting, and standing positions using the new device was evaluated. Transient decrease in blood pressure within 15 s after rising to an erect position possibly causes dizziness, syncope, and fall. Subjects exhibiting dizziness upon standing showed a significant decrease in the cephalic blood flow (CBF) and indirect beat-to-beat systolic blood pressure, as monitored by the Finometer, and a significant correlation was observed between the drop ratio (drop value on rising/mean value in the squatting position) of CBF and that of systolic blood pressure.

CONCLUSIONS

This new wearable CBF-meter is potentially useful for estimating cephalic hemodynamics and objectively diagnosing cerebral ischemic symptoms of subjects in a standing posture.

Endothelial function and oxidative stress in cardiovascular diseases

The vascular endothelium is involved in the release of various vasodilators, including nitric oxide (NO), prostacyclin and endothelium-derived hyperpolarizing factor, as well as vasoconstrictors. NO plays an important role in the regulation of vascular tone, inhibition of platelet aggregation, and suppression of smooth muscle cell proliferation. Endothelial dysfunction is the initial step in the pathogenesis of atherosclerosis. Cardiovascular diseases are associated with endothelial dysfunction. It is well known that the grade of endothelial function is a predictor of cardiovascular outcomes. Oxidative stress plays an important role in the pathogenesis and development of cardiovascular diseases. Several mechanisms contribute to impairment of endothelial function. An imbalance of reduced production of NO or increased production of reactive oxygen species, mainly superoxide, may promote endothelial dysfunction. One mechanism by which endothelium-dependent vasodilation is impaired is an increase in oxidative stress that inactivates NO. This review focuses on recent findings and interaction between endothelial function and oxidative stress in cardiovascular diseases.

Relationship between augmentation index and flow-mediated vasodilation in the brachial artery

Recent studies have shown that the augmentation index (AI) is a predictor of cardiovascular complications. Endothelial dysfunction is the initial step in the pathogenesis of atherosclerosis, which in turn can lead to cardiovascular complications. Endothelial function assessed by flow-mediated dilation (FMD) can serve as an independent predictor of cardiovascular events. However, there is little information on the relationship between AI and FMD in the human vasculature, and we therefore investigated this relationship in the present study. A total of 100 subjects (71 males and 29 females; age range, 22-88 years; mean age, 59 +/- 17 years), including 83 patients with cardiovascular diseases (e.g., atherosclerosis, hypertension, coronary heart disease, stroke and peripheral arterial disease) and 17 healthy subjects were enrolled. High-resolution ultrasonography (automated vessel-diameter measurements; eTRACKING system), a linear array transducer (13 MHz) and an arm holding device were used to measure the arterial diameter response to reactive hyperemia and sublingual nitroglycerine (NTG, 75 micrograms) in all subjects. AI measured using an automated device was significantly correlated with FMD (r = -0.38, p < 0.0001). There was no significant correlation between AI and vascular response to NTG. Multiple regression analysis showed that FMD was a significant independent predictor of AI (p < 0.05). These findings suggest that increase in arterial stiffness may be associated with grade of endothelial dysfunction and that AI may be an index of not only arterial stiffness but also endothelial function.

Whole-body periodic acceleration enhances brachial endothelial function

BACKGROUND

Periodic acceleration in the direction of the spinal axis through repetitive movement increases the shear stress on the vascular endothelium. In the present study it was assessed whether whole-body periodic acceleration with a new device would enhance endothelial function in sedentary adult volunteers.

METHODS AND RESULTS

Twenty-six sedentary subjects (44+/-3 years) were randomly assigned to remain sedentary or perform exercise training for 4 weeks, followed by crossover. Periodic acceleration was applied with a horizontal motion platform at 2-3 Hz and approximately +/-2.2 m/s2 for 45 min. Increases in the brachial artery diameter were examined at rest, during reactive hyperemia (flow-mediated dilatation: %FMD) and after sublingual administration of 0.3 mg nitroglycerin (%NTG) using high-resolution ultrasound. All subjects completed the study with no adverse side-effects. There were no significant changes in the resting heart rate or arterial pressure, body weight, or lipid profiles during the study. Although %FMD did not change during the non-training period with periodic acceleration, it significantly increased from 7.3+/-0.4% at baseline to 8.4+/-0.4% after the training period (p<0.05), while %NTG remained unchanged.

CONCLUSIONS

Whole-body periodic acceleration with a horizontal motion platform improved vascular endothelial function in sedentary adults. This device might offer an alternative to active exercise for patients whose medical condition limits physical activity.